1,5-anhydroglucitol (hereinafter, referred to as 1,5-AG) is present in human body fluids such as serum, plasma and urine and largely varies in amount in body fluids due to a certain kind of disease, particularly, diabetes mellitus. Therefore, assay values of 1,5-AG in body fluids serve as a useful diagnostic index and have been an important test item in clinical test in recent years.
As a method for quantifying this 1,5-AG, a method described in, for example, PATENT DOCUMENT 1 is in the mainstream which comprises allowing pyranose oxidase to act on 1,5-AG and subjecting the formed hydrogen peroxide to colorimetry in a peroxidase chromogenic system. This method has been practiced using a general-purpose automatic analyzer.
For example, a method described in PATENT DOCUMENT 2 is known as an alternative assay method, which comprises allowing a 1,5-AG-phosphorylating enzyme to act on 1,5-AG in the presence of a phosphate group donor and subjecting the obtained 1,5-AG-6-phosphate to colorimetry using 1,5-AG-6-phosphate dehydrogenase.
Moreover, a method for assaying 1,5-AG using 1,5-AG dehydrogenase has also been reported in PATENT DOCUMENTS 3 to 5. Agrobacterium tumefaciens-derived dehydrogenase described in PATENT DOCUMENTS 4 and 5, Cytophaga bacterium-derived dehydrogenase described in PATENT DOCUMENT 6, Rahnella aquatilis-, Enterobacter cloacae- or Serratia marcescens-derived dehydrogenase described in PATENT DOCUMENT 7, dehydrogenase derived from fungi such as Eupenicillium crustaceum, Hansenula california, Pichia carsonii and Pichia pseudopolymorpha described in PATENT DOCUMENT 8, Trichoderma longibrachiatum-derived dehydrogenase described in PATENT DOCUMENT 9, and the like have been reported as dehydrogenases acting on 1,5-AG.